The invention relates to a pressure-fluid operated ride leveler allowing for the free selection of the desired level, in particular for use in vehicles.
A pressure-fluid operated ride leveler is known from DE 30 39 345 C2.
If the body of a vehicle equipped with this known ride leveler is to be lifted from a normal level (defined as a predetermined mean distance between vehicle axle and vehicle body) to a higher level (greater distance between vehicle axle and vehicle body), the driver moves a switch of an operating unit into "Lifting" position. The pressure fluid chambers of pressure-fluid-operated shock absorbers are then connected via a valve mechanism to a pressure fluid source. The pressure fluid flowing into the pressure fluid chambers produces an increase in the distance between the vehicle axle and the vehicle body. The desired level is compared with the actual level by means of sensors. If the desired level equals the actual level, the valve mechanism is caused to break the connection between the pressure fluid source and the pressure fluid chambers.
If the vehicle is to be lowered to a lower level, the amount of pressure fluid in the pressure fluid chambers is decreased via the valve mechanism into the atmosphere or to a sump.
To be able to carry out the "Lifting" and "Lowering" processes rapidly, it is necessary to use pressure fluid conduits with large diameters. Due to the rapid change in volume of pressure fluid in the pressure fluid chambers, it cannot be avoided that pressure fluid will continue to flow into the pressure fluid chambers or out of the pressure fluid chambers at the moment when equality between the desired level and the actual level is detected and the valve mechanism is actuated. As a consequence, the actual level becomes greater than the desired level during the "Lifting" process and the actual level becomes less than the desired level during the "Lowering" process. The distance between vehicle axle and vehicle body is thus greater or less than the desired distance.
In order to obtain a desired predetermined distance between vehicle axle and vehicle body, it is necessary for the above-mentioned reasons to follow an input of pressure fluid into the pressure fluid chambers during the "Lifting" process with a minor reduction of the pressure fluid in the pressure fluid chambers. Similarly, it is necessary to follow a pressure fluid reduction during the "Lowering" process with a minor addition of pressure fluid into the pressure fluid chambers. It may also be necessary to repeat this process until the actual level is equal to the desired level.
Due to this control correction, adjustment of the level of the vehicle cabin is uneven and in vehicles used for passenger transportation it is uncomfortable to the passengers. Furthermore, in air-cushioned vehicles, the air consumption is increased.
It is the object of the instant invention to improve a ride leveler of the type mentioned above in such manner that the desired level is attained with the least possible number of adjustment steps.